The present application relates to a current generating circuit/method and a charge pumping circuit/method, and particularly relates to a current generating circuit/method that can substitute a conventional current generating circuit/method and a charge pumping circuit/method applying the current generating circuit/method.
FIG. 1A is a diagram of a conventional charge pumping circuit 100. The conventional charge pumping circuit 100 includes a pull up circuit 101 and a pull down circuit 102, and both of the circuits are used to adjust a control voltage V_CT there between. The control voltage V_CT is further used as an output voltage of the conventional charge pumping circuit 100, and it may be applied to other external circuits (ex. coupled to a capacitor for providing a desired voltage).
FIG. 1B is a schematic diagram illustrating a narrow head room issue for a conventional charge pumping circuit 100. Since the control voltage V_CT directly affects the operation states of transistors in the pull up circuit 101 and the pull down circuit 102, the control voltage V_CT should be limited within a specific operating range so as to make the transistors operate in an appropriate work mode, such as a saturation mode. Generally, if the conventional charge pumping circuit 100 operates between a high predetermined voltage V_DD (ex. a supplying voltage) and a low predetermined voltage V_SS (ex. a ground voltage) and each transistor therein has an overdrive voltage V_OV, the control voltage V_CT should be limited by an upper boundary, which is the high predetermined voltage V_DD minus the overdrive voltage V_OV, and a lower boundary, which is the low predetermined voltage V_SS plus the overdrive voltage V_OV. In other words, the operating range of the control voltage V_CT is substantially equal to the high predetermined voltage V_DD minus two times the overdrive voltage V_OV (i.e. V_DD−2×V_OV), and it is extremely narrow and not suitable for some circuit applications. Such issue is called a narrow head room issue.
Either the pull up circuit 101 or the pull down circuit 102 comprises a current source to provide a current. However, such current sources may generate noises. One method for reducing the noise is increasing the overdrive voltage V_OV. However, such mechanism can make the narrow head room issue worse.